Recently, field effect transistors (FETs) such as metal oxide semiconductor field effect transistors (MOSFETs) or junction field effect transistors (JFETs) have achieved a great deal of advance in their performance and manufacturing process technology. The field-effect transistor is a transistor that relies on an electric field to control the shape of the nonconductive depletion layer within a semiconductor material, thus controlling the conductivity of a channel in that material. In other words, once a voltage is applied between the gate region and the source layer, the current is controlled to flow vertically from the drain region to the source layer with the gate region in between. Like all transistors, field-effect transistors can be used as voltage-controlled variable resistors or voltage controlled current sources.
The junction field-effect transistor (JFET) uses voltage applied across a reverse-biased PN junction between the gate region and the source/drain region to control the width of the depletion region, which then controls the conductivity of a semiconductor channel. The metal oxide semiconductor field effect transistor (MOSFET) is a field-effect transistor having a metallic gate insulated from the channel by an oxide layer and the channel conductivity thereof is dependent only on the potential at the gate region.
The MOSFET device is extensively used in digital circuits because the structure thereof is developed toward minimization and it is a very efficient switch. As such, it is possible to fabricate a great number of MOS transistors in a single chip. The structure of the junction field-effect transistor (JFET) is distinguished from the metal oxide semiconductor field effect transistor (MOSFET). Due to the structure difference, the junction field-effect transistors (JFETs) are typically used as analog switches or signal amplifiers, especially low-noise amplifiers, but seldom used as logical operation units or power amplifiers.
Due to the specific structure, the conventional junction field-effect transistor (JFET) fails to handle large current for power management purposes. It is important to modify and regulate the structure and the manufacturing process of the junction field-effect transistor (JFET) so as to overcome the above-described disadvantages resulted from the prior art.